Design-Based weighting for logic built-in self-test

ABSTRACT

Embodiments relate to design-based weighting for logic built-in self-test (LBIST). An aspect includes a computer program product for implementing design-based weighting for LBIST. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes analyzing, by the processing circuit, a plurality of integrated circuit design organizational units to determine preferred weightings of the integrated circuit design organizational units that provide a highest level of failure coverage when applied to a random pattern generator. Based on determining the preferred weightings, the processing circuit creates an integrated circuit layout that includes a plurality of weighted test paths to respectively apply the preferred weightings to the integrated circuit design organizational units. The integrated circuit layout is incorporated in a device under test.

DOMESTIC PRIORITY

This application is a continuation of U.S. application Ser. No.14/105,285 filed Dec. 13, 2013, the disclosure of which is incorporatedby reference herein in its entirety.

BACKGROUND

The present invention relates generally to integrated circuit testing,and more specifically, to design-based weighting for logic built-inself-test (LBIST).

LBIST is used to test integrated circuit logic of high-end servers andcomputers. LBIST is used at all levels of test including: integratedcircuit, multi-chip module (MCM), and system levels. Conceptually, theLBIST approach is based on the realization that much of a circuittester's electronics is semi-conductor based, just like the devicesunder test, and that many of the challenges and limitations of testinglie in the interface to the Device Under Test (DUT). The LBIST approachcan be described as an attempt to move many of the alreadysemiconductor-based test equipment functions into the DUT and eliminatecomplex interfacing. One of the major advantages LBIST has over othermeans of testing logic is that operation of the test is self-contained.All of the circuitry required to execute the test at-speed is containedwithin the integrated circuit. Very limited external controls areneeded, so LBIST can be run at all levels of packaging (e.g., wafer,module and system) without requiring expensive external test equipment.

LBIST utilizes what is commonly referred to as Self-Test Using MultipleSignal Registers and Pseudo-Random Pattern Generators (STUMPS)architecture. The major components of LBIST include: a pseudo-randompattern generator (PRPG) used to generate the test patterns; a multipleinput signature register (MISR) to compress the test results; and theself-test control macro (STCM) that is used to apply clocks and controlsto the PRPG, MISR and system logic to perform the test. The PRPG appliestest data to the system logic via multiple parallel scan chains, whichare connected between the PRPG and MISR.

One of the limitations of LBIST is the maximum achievable test coverage.Because the PRPG is implemented using a linear feedback shift register(LFSR) that generates random patterns (i.e., 50% chance of being a 0 ora 1), certain random resistant structures are difficult, if notimpossible, to test. Examples include very wide AND gates or OR gateswhere the probability of all inputs being a 1 in the case of an AND gateor all inputs being a 0 in the case of an OR gate is very small.Typically, LBIST test coverage peaks at around 96%. The remaining faultsmust be tested by some other means of logic test, either weighted randompattern test (WRPT), deterministic test, or a combination of both.

Weighting is a technique where patterns can be biased towards a 0 or 1state by ANDing or ORing multiple bits of an LFSR together. Instead of a50% chance of a 0 or a 1, the odds of a 0 or 1 are weighted to increasethe probability of one or the other occurring. For example, if 3 randombits are ORed together, the resultant output has a 7/8 chance of beinga 1. Conversely, if 4 random bits are ANDed together, the output has a1/16 chance of being a 1. This weighting technique can be used to testrandom resistant structures such as large AND or OR structures.

In contemporary designs, many LBIST variations are used in manufacturingtests employing different weights. As one example, U.S. Pat. No.6,671,838, “Method and Apparatus for Programmable LBIST ChannelWeighting” filed Sep. 27, 2000, which is incorporated herein byreference, teaches a built-in self-test (BIST) method and apparatus fortesting logic circuits on an integrated circuit, where a randomresistant fault analysis (RRFA) program is used to determine weightingrequirements on a per channel basis. In U.S. Pat. No. 6,671,838,weighting requirements from the RRFA program are applied to random testpattern data resulting in weighted test pattern data that isprogrammably applied to a scan chain.

SUMMARY

An aspect includes a computer program product for implementingdesign-based weighting for logic built-in self-test (LBIST). Thecomputer program product includes a tangible storage medium readable bya processing circuit and storing instructions for execution by theprocessing circuit for performing a method. The method includesanalyzing, by the processing circuit, a plurality of integrated circuitdesign organizational units to determine preferred weightings of theintegrated circuit design organizational units that provide a highestlevel of failure coverage when applied to a random pattern generator.Based on determining the preferred weightings, the processing circuitcreates an integrated circuit layout that includes a plurality ofweighted test paths to respectively apply the preferred weightings tothe integrated circuit design organizational units. The integratedcircuit layout is incorporated in a device under test.

According to another aspect, a computer-implemented method forimplementing design-based weighting for LBIST includes analyzing, by aprocessing circuit, a plurality of integrated circuit designorganizational units to determine preferred weightings of the integratedcircuit design organizational units that provide a highest level offailure coverage when applied to a random pattern generator. Based ondetermining the preferred weightings, the processing circuit creates anintegrated circuit layout that includes a plurality of weighted testpaths to respectively apply the preferred weightings to the integratedcircuit design organizational units. The integrated circuit layout isincorporated in a device under test.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as embodiments is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe embodiments are apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 depicts a system for providing design-based weighting for logicbuilt-in self-test in accordance with an embodiment;

FIG. 2 depicts a design structure in accordance with an embodiment;

FIG. 3 depicts another design structure in accordance with anembodiment;

FIG. 3A depicts a variation of the design structure of FIG. 3 inaccordance with an embodiment;

FIG. 4 depicts an alternate embodiment of the design structure of FIG. 3in accordance with an embodiment;

FIG. 5 depicts an additional design structure in accordance with anembodiment;

FIG. 6 depicts a further design structure in accordance with anembodiment;

FIG. 7 depicts a process flow for implementing design-based weightingfor logic built-in self-test in accordance with an embodiment;

FIG. 8 illustrates a computer program product in accordance with anembodiment; and

FIG. 9 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION

In exemplary embodiments, design-based weighting for logic built-inself-test (LBIST) is provided, where preferred weightings of theintegrated circuit design organizational units are determined and anintegrated circuit layout is created based on the preferred weightings.Rather than analyzing a design after the integrated circuit layout isfinalized, embodiments perform analysis during the design process andensure that preferred weightings are included. Where the integratedcircuit design organizational units are macros, the macros can beassigned to scan chains or LBIST channels that include the preferredweighting of each respective macro. If the integrated circuit designorganizational units are Self-Test Using Multiple Signal Registers andPseudo-Random Pattern Generators (STUMPS) channels, the analyzing can beperformed on a STUMPS channel basis, and the integrated circuit layoutis updated to include the preferred weightings of each STUMPS channel.

In one embodiment, design for test (DFT) macro analysis is used todetermine the preferred weightings per macro during an integratedcircuit design process. The macros can be assigned to STUMPS channelsthat enable each macro to receive its preferred weighting as test inputbased on the preferred weightings determined during the DFT macroanalysis. The preferred weightings represent weightings that provide ahighest level of test coverage. By first learning the preferredweightings and then establishing an integrated circuit layout thatenables routing of the preferred weightings to respective integratedcircuit design organizational units, LBIST patterns can achieve a higherpercentage of test coverage. The preferred weightings need not belimited to only a few options, such as 1/8 weighting and 7/8 weighting,but can include arbitrary weightings that provide the highest level oftest coverage, such as a 1/16 weighting, 15/16 weighting, 1/32weighting, 31/32 weighting, and so forth.

In another embodiment, the DFT analysis is performed after the STUMPSchannels are assigned. In this case, the DFT analysis is done on theexisting STUMPS channels, and the preferred weightings are establishedbased on this data. The preferred weightings can be hard coded for eachSTUMPS channel or provided as a selectable input, e.g. as a multiplexerinput, where other non-weighted inputs or non-preferred weighted inputscan also be made available for testing.

In a further embodiment, after determining preferred weightings for adesign, a complete LBIST channel can be assigned for each uniqueinstance of the preferred weightings. Integrated circuit designorganizational units, such as macros, can be assigned to a correspondingLBIST channel based on the preferred weightings of the respectivemacros.

Turning now to FIG. 1, a system 100 is generally shown that includes anintegrated circuit (IC) development system 102 configured to incorporatean integrated circuit layout into a device under test (DUT) 112. The ICdevelopment system 102 can fabricate the DUT 112 as an integratedcircuit chip. The DUT 112 can be distributed by the fabricator in rawwafer form (that is, as a single wafer that has multiple unpackagedchips), as a bare die, or in a packaged form. In the latter case the DUT112 can be mounted in a single chip package (such as a plastic carrier,with leads that are affixed to a motherboard or other higher levelcarrier) or in a multichip package (such as a ceramic carrier that haseither or both surface interconnections or buried interconnections). TheDUT 112 may also be integrated with other chips, discrete circuitelements, and/or other signal processing devices as part of either (a)an intermediate product, such as a motherboard, or (b) an end product.The end product can be any product that includes integrated circuitchips, ranging from toys and other low-end applications to advancedcomputer products having a display, a keyboard or other input device,and a central processor. An exemplary design flow for developing the DUT112 is described in greater detail herein with respect to FIG. 9.

Continuing with the description of FIG. 1, the IC development system 102includes a processing circuit 104 and a memory system 106. Theprocessing circuit 104 can be any type of processor or microcontroller,including multiple instances thereof, that is configurable to executeprocesses further described herein, where the memory system 106 is anexample of a tangible storage medium. The memory system 106 can includeIC development tools 108 and design files 110. The IC development tools108 may be partitioned as one or more computer program products. Forexample, the IC development tools 108 can include a DFT analyzer 114 anda random pattern generator 116 among other executable applications (notdepicted). The design files 110 can include definition files for aplurality of integrated circuit design organizational units 118, such asSTUMPS channels 120 and macros 122. The STUMPS channels 120 can includethe macros 122 organized in scan chains. The macros 122 define logiccircuits that can include latches and logic blocks (e.g., logic gates)organized to implement a particular function, such as an arithmeticlogic unit macro, an error checking macro, a decoding macro, etc.

In an exemplary embodiment, the processing circuit 104 is coupled to thememory system 106, and the processing circuit 104 is configured toexecute the IC development tools 108 to analyze a plurality ofintegrated circuit design organizational units 118 defined in the designfiles 110 to determine preferred weightings of the integrated circuitdesign organizational units 118 that provide a highest level of failurecoverage when applied to the random pattern generator 116 of the ICdevelopment tools 108. For example, the DFT analyzer 114 can iterateover a large range of possible weightings to identify the preferredweightings of the integrated circuit design organizational units 118,e.g., 1/2, 1/4, 3/4, 1/8, 7/8, 1/16, 15/16, 1/32, 31/32, 1/64, 63/64,1/128, 127/128, 1/256, 255/256, and so forth. Based on determining thepreferred weightings, the processing circuit 104 creates an integratedcircuit layout 124 that includes a plurality of weighted test paths torespectively apply the preferred weightings to the integrated circuitdesign organizational units 118. The integrated circuit layout 124 canbe stored in the design files 110, and at least one of the design files110 associated with the integrated circuit layout 124 can be modified toannotate the preferred weightings of the integrated circuit designorganizational units 118 in the design files 110. The integrated circuitlayout 124 is incorporated in the DUT 112, for example, as a designstructure as described herein with respect to FIG. 9.

FIG. 2 depicts a design structure 200 in accordance with an embodiment.The design structure 200 illustrates a portion of the DUT 112 of FIG. 1as a block diagram. The design structure 200 of FIG. 2, includes apseudo-random pattern generator (PRPG) 202 including a linear feedbackshift register (LFSR) 204 that generates random patterns (i.e., 50%chance of being a 0 or a 1) and distributes the random patterns via aspreading network 206 to a plurality of scan chains 208 a, 208 b, . . ., 208 m, 208 n. The scan chains 208 a-208 n provide test paths throughpartial or complete instances of the macros 122 of FIG. 1 as embodied inthe DUT 112 of FIG. 1. A multiple input signature register (MISR) 210compresses the test results to confirm that failures are detected in asummarized format. Although several examples provided herein refer touse of a MISR, other result compression structures known in the art canbe substituted in various embodiments, such as an XOR compressionregister. Exemplary embodiments include incorporating preferredweightings for the scan chains 208 a-208 n into the design structure 200to provide a highest level of fault coverage over a shortest amount oftime. The preferred weightings may be integrated into the spreadingnetwork 206 such that each of the scan chains 208 a-208 n receives itspreferred weighting.

FIG. 3 depicts another design structure 300 in accordance with anembodiment. In the example of FIG. 3, the design structure 300, whichmay be implemented in the DUT 112 of FIG. 1, includes an LFSR 304, aspreading network 306, and a plurality of scan chains 308 a-308 n. Aplurality of multiplexers 312 a-312 n are incorporated in the spreadingnetwork 306 to establish different weightings for scan chains 308 a-308n. Each combination of a multiplexer 312 and a scan chain 308 may bereferred to as a STUMPS channel 314. Accordingly, the example of FIG. 3includes STUMPS channels 314 a-314 n. Each of the multiplexers 312 has anumber of multiplexer inputs 316.

As depicted in FIG. 3, multiplexer 312 a includes four multiplexerinputs 316 a as a 1/8 weighted input, a 7/8 weighted input, anon-weighted input, and a preferred weighting input. The 1/8 weightedinput of the multiplexer inputs 316 a may be generated by an AND-gate318 a, as only one of eight possible input combinations results in alogical ‘1’. The 7/8 weighted input of the multiplexer inputs 316 a maybe generated by an OR-gate 320 a, as seven of eight possible inputcombinations result in a logical ‘1’. A direct link 322 a between theLFSR 304 and the multiplexer 312 a provides a non-weighted input with animplied weighting of 1/2, as the LFSR 304 generates random patterns witha 50% chance of a logical ‘1’. A preferred weighting 324 a can begenerated in a similar manner as the 1/8 and 7/8 weights, such as a fourinput AND-gate for a 1/16 weight or a five input OR-gate for a 31/32weight, etc. It will be understood that any circuit capable of producinga weighting can be used in various embodiments as described herein, andweighting (preferred or otherwise) is not limited to the use ofAND-gates and OR-gates. A weighted test path 326 a is defined betweenthe LFSR 304, the preferred weighting 324 a, the multiplexer 312 a, andthe scan chain 308 a to apply to the preferred weighting 324 a to theintegrated circuit design organizational units 118 of FIG. 1 embodied inthe scan chain 308 a.

A similar layout is repeated in the design structure 300 to testadditional STUMPS channels 314. For example, for STUMPS channel 314 n,multiplexer 312 n includes four multiplexer inputs 316 n as a 1/8weighted input, a 7/8 weighted input, a non-weighted input, and apreferred weighted input. The multiplex inputs 316 n are generated byAND-gate 318 n, OR-gate 320 n, direct link 322 n, and preferredweighting 324 n. A weighted test path 326 n is defined between the LFSR304, the preferred weighting 324 n, the multiplexer 312 n, and the scanchain 308 n to apply to the preferred weighting 324 n to the integratedcircuit design organizational units 118 of FIG. 1 embodied in the scanchain 308 n. While each of the multiplexers 312 a-312 n are depicted ashaving the same multiplexer inputs 316 a-316 n at the same multiplexerinput position, i.e., 1/8, 7/8, 1/2, and preferred weighting positions,the values of the preferred weightings 324 a-324 n can vary. Forexample, the preferred weightings 324 a and 324 n may both be assignedas at a first multiplexer input position (e.g., channel 0) on respectivemultiplexers 312 a and 312 n, the weighting values produced by thepreferred weightings 324 a and 324 n can be different, such as 15/16 and1/64. Each multiplexer 312 a-312 n may have a respective weightselection register 328 a-328 n to enable independent routing of weightsper STUMPS channel 314 a-314 n.

If a given integrated circuit design has a large number of differentpreferred weightings, e.g., more than four, modifying the IC layout 124of FIG. 1 to align the preferred weightings with correspondingintegrated circuit design organizational units 118 of FIG. 1 results ina greater level of test coverage while also keeping the multiplexers 312a-321 n and respective weight selection registers 328 a-328 n relativelycompact such that each STUMPS channel 314 a-314 n need not support allweighting permutations. While only four multiplexer inputs 316 a-316 nare depicted for each multiplexer 312 a-312 n with specific exampleweights provided, it will be understood the multiplexer 312 a-312 n cansupport a different number of multiplexer inputs 316 a-316 n withdifferent weights beyond those depicted in FIG. 3. For example,different or additional weights such as 1/4, 3/4, 1/16, 15/16, 1/32,31/32, etc. can be included in various embodiments. Furthermore, asdepicted in the example of FIG. 3A, fewer multiplexer inputs 316 a-316 n(e.g., two) can be provided to each multiplexer 312 a-312 n. Uponincorporating the preferred weightings 324 a and 324 n, other weightscan be removed from the spreading network 306, such as the 1/8 and 7/8weighted inputs (see FIG. 3 vs. FIG. 3A) to reduce overall LBISTcircuitry and use narrower instances of the multiplexer 312 a-312 n andweight selection registers 328 a-328 n.

FIG. 4 depicts an alternate embodiment of the design structure 300 ofFIG. 3 in accordance with an embodiment as design structure 400. Similarto the design structure 300 of FIG. 3, the design structure 400 of FIG.4 includes LFSR 304, spreading network 306, scan chains 308 a-308 n,multiplexers 312 a-312 n, STUMPS channels 314 a-314 n, multiplexerinputs 316 a-316 n, AND-gates 318 a-318 n, OR-gates 320 a-320 n, directlinks 322 a-322 n, preferred weightings 324 a-324 n, and weighted testpaths 326 a-326 n. Where the same multiplexer inputs 316 a-316 n arerouted to the same multiplexer input position, i.e., 1/8, 7/8, 1/2, andpreferred weighting positions, on the multiplexers 312 a-312 n, a commonweight selection register 428 can be used for two or more of themultiplexers 312 a-312 n. In the example of FIG. 4, the preferredweightings 324 a-324 n are assigned to a same multiplexer input positionacross a plurality of multiplexers 312 a-314 n such that selection ofthe same multiplexer input position for the multiplexers 312 a-314 nresults in selecting the preferred weightings 324 a-324 n across themultiplexers 312 a-312 n at the same time.

The common weight selection register 428 can further increase test speedas fewer write operations may be needed to establish a particulartesting mode. For instance, a preferred weighting testing mode can bedefined as selecting the preferred weighting 324 a-324 n from at leasttwo of the multiplexers 312 a-312 n at the same multiplexer inputposition at the same time. While only four multiplexer inputs 316 a-316n are depicted for each multiplexer 312 a-312 n with specific exampleweights provided, it will be understood the multiplexer 312 a-312 n cansupport a different number of multiplexer inputs 316 a-316 n withdifferent weights beyond those depicted in FIG. 4. Similar to FIG. 3A,fewer multiplexer inputs 316 a-316 n (e.g., two) can be provided to eachmultiplexer 312 a-312 n including, for instance, only the direct links322 a-322 n and preferred weightings 324 a and 324 n.

FIG. 5 depicts an additional design structure 500 in accordance with anembodiment. The design structure 500 illustrates an embodiment of aportion of the DUT 112 of FIG. 1 as a block diagram. Similar to theexample of FIG. 2, the design structure 500 of FIG. 5 includes an LFSR504 that generates random patterns (i.e., 50% chance of being a 0 ora 1) and distributes the random patterns via a spreading network 506 toa plurality of scan chains 508 a, 508 b, . . . , 508 m, 508 n. The scanchains 508 a-508 n provide weighted test paths through various macros122 of FIG. 1 as embodied in the DUT 112 of FIG. 1. The MISR 510compresses the test results to confirm that failures are detected in asummarized format.

When DFT analysis is performed using the STUMPS channels 120 of FIG. 1as the integrated circuit design organizational units 118 of FIG. 1, thescan chains 508 a-508 m may already have instances of the macros 122 ofFIG. 1 assigned to them. In the example of FIG. 5, scan chain 508 aincludes macro mac_a, scan chain 508 b includes macro mac_b, scan chain508 m includes mac_m, and scan chain 508 n includes macro mac_n. Whenthe DFT analysis is performed by DFT analyzer 114 of FIG. 1 on a STUMPSchannel basis, the IC layout 124 of FIG. 1 can be created as amodification that assigns preferred weightings based on an existinglayout rather than reallocating the macros 122 of FIG. 1. At least oneof the design files 110 of FIG. 1 may be annotated to include thepreferred weightings on a STUMPS channel basis. The IC layout 124 ofFIG. 1 can be created or modified based on the annotations to layout thespreading network 506 to provide the preferred weightings to each of thescan chains 508 a-508 n. AND-gate or OR-gate combinations can be laidout in the spreading network 506 to hard code the preferred weightings.For example, if mac_a of scan chain 508 a and mac_n of scan chain 508 nprefer a 1/2 weight (i.e., non-weighted), then the spreading network 506layout can provide direct links from the LFSR 504 to scan chains 508 aand 508 n. If mac_b of scan chain 508 b has a preferred weighting of15/16, then the spreading network 506 layout can include an appropriatecircuit (e.g., 4-input OR-gate) between the LFSR 504 and scan chain 508b to form a weighted test path 526 b. Similarly, if mac_m of scan chain508 m has a preferred weighting of 1/16, then the spreading network 506layout can include an appropriate circuit (e.g., 4-input AND-gate)between the LFSR 504 and scan chain 508 m to form a weighted test path526 m.

FIG. 6 depicts a further design structure 600 in accordance with anembodiment. The design structure 600 illustrates an embodiment of aportion of the DUT 112 of FIG. 1 as a block diagram. In FIG. 6, separateLBIST channels 602 for each unique instance of the preferred weightingsare created, and the macros 122 of FIG. 1 are assigned to acorresponding LBIST channel 602 based on the preferred weightings of themacros 122 of FIG. 1. For example, if four scan chains are determined tohave a preferred weighting of 1/4 and LBIST channel 602 a corresponds toa preferred weighting of 1/4, then spreading network 606 a would includea preferred weighting of 1/4 (e.g., a 2-input AND-gate) between LFSR 604a and each scan chain 608 a-608 d, with test results captured in MISR610 a. If three scan chains are determined to have a preferred weightingof 63/64 and LBIST channel 602 n corresponds to a preferred weighting of63/64, then spreading network 606 n would include a preferred weightingof 63/64 (e.g., a 6-input OR-gate) between LFSR 604 n and each scanchain 608 n-608 p, with test results captured in MISR 610 p.

Accordingly, with respect to the example of FIG. 6, the integratedcircuit layout 124 of FIG. 1 includes weighted test paths 626 a-626 d torespectively apply the preferred weightings (i.e., 1/4) to the macros122 of FIG. 1 embodied in the scan chains 608 a-608 d. The integratedcircuit layout 124 of FIG. 1 also includes weighted test paths 626 n-626p to respectively apply the preferred weightings (i.e., 63/64) to themacros 122 of FIG. 1 embodied in the scan chains 608 n-608 p in thisexample. The example continues for all unique preferred weightings inthe DUT 112 of FIG. 1.

FIG. 7 depicts a computer-implement process 700 for implementingdesign-based weighting for logic built-in self-test in accordance withan embodiment. The process 700 can be implemented by the IC developmentsystem 102 of FIG. 1 to incorporate one or more of the design structures200-600 of FIGS. 1-6 into the DUT 112 of FIG. 1. The process 700 isdescribed with respect to FIGS. 1-7.

At block 702, a plurality of integrated circuit design organizationalunits 118 are analyzed to determine preferred weightings of theintegrated circuit design organizational units 118 that provide ahighest level of failure coverage when applied to the random patterngenerator 116. The analysis can be performed by the DFT analyzer 114.The integrated circuit design organizational units 118 may be analyzedas macros 122 prior to organizing the macros into STUMPS channels 120 oranalyzed as STUMPS channels 120 after assignment of the macros 122 tothe STUMPS channels 120.

At block 704, based on determining the preferred weightings, theprocessing circuit 104 creates an IC layout 124 that includes aplurality of weighted test paths to respectively apply the preferredweightings to the integrated circuit design organizational units 118.For example, the preferred weightings 324 a-324 n can be applied toSTUMPS channels 314 a-314 n via weighted test paths 326 a-326 n. Thepreferred weightings 324 a-324 n can be assigned to multiplexer inputs316 a-316 n for the weighted test paths 326 a-326 n. Connecting a commonweight selection register 428 to at least two of the multiplexers 312a-312 n can enable selection of the same multiplexer input position forthe at least two of the multiplexers 312 a-312 n at a same time. Atleast one of the design files 110 can be modified to annotate thepreferred weightings of the integrated circuit design organizationalunits 118 in the design files 110, e.g., at a macro level or STUMPSchannel level. Where multiple LBIST channels 602 a-602 n are used, anLBIST channel 602 a-602 n can be assigned to each unique instance of thepreferred weightings, and the macros 122 assigned to a correspondingLBIST channel 602 a-602-n based on the preferred weightings of themacros 122. At block 706, the IC layout 124 is incorporated in the DUT112.

Technical effects and benefits include design-based weighting for logicbuilt-in self-test, where integrated circuit design organizational unitsare analyzed to determine preferred weightings, and based on thepreferred weightings an integrated circuit layout is created including aplurality of weighted test paths to respectively apply the preferredweightings to the integrated circuit design organizational units.

As will be appreciated by one of average skill in the art, aspects ofembodiments may be embodied as a system, method or computer programproduct. Accordingly, aspects of embodiments may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as, for example, a “circuit,” “module” or “system.”Furthermore, aspects of embodiments may take the form of a computerprogram product embodied in one or more computer readable storagedevice(s) having computer readable program code embodied thereon.

One or more of the capabilities of embodiments can be implemented insoftware, firmware, hardware, or some combination thereof. Further, oneor more of the capabilities can be emulated.

Referring to FIG. 8, one or more aspects of embodiments can be includedin an article of manufacture (e.g., one or more computer programproducts 800) having, for instance, computer readable storage media 802.The media has embodied therein, for instance, computer readable programcode (instructions) 804 to provide and facilitate the capabilities ofembodiments. The article of manufacture can be included as a part of acomputer system or as a separate product. For example, the memory system106 of FIG. 1 can be or include an embodiment of the computer readablestorage media 802, where the IC development tools 108 of FIG. 1 areembodied as computer readable program code 804 for execution by theprocessing circuit 104 of FIG. 1.

An embodiment may be a computer program product for enabling processorcircuits to perform elements of the invention, the computer programproduct comprising a computer readable storage medium readable by aprocessing circuit and storing instructions for execution by theprocessing circuit for performing a method.

The computer readable storage medium (or media), being a tangible,non-transitory, storage medium having instructions recorded thereon forcausing a processor circuit to perform a method. The “computer readablestorage medium” being non-transitory at least because once theinstructions are recorded on the medium, the recorded instructions canbe subsequently read one or more times by the processor circuit at timesthat are independent of the time of recording. The “computer readablestorage media” being non-transitory including devices that retainrecorded information only while powered (volatile devices) and devicesthat retain recorded information independently of being powered(non-volatile devices). An example, non-exhaustive list of“non-transitory storage media” includes, but is not limited to, forexample: a semi-conductor storage device comprising, for example, amemory array such as a RAM or a memory circuit such as latch havinginstructions recorded thereon; a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon; an optically readable device such as a CD or DVDhaving instructions recorded thereon; and a magnetic encoded device suchas a magnetic tape or a magnetic disk having instructions recordedthereon.

A non-exhaustive list of examples of computer readable storage mediuminclude the following: a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), a portablecompact disc read-only memory (CD-ROM). Program code can be distributedto respective computing/processing devices from an external computer orexternal storage device via a network, for example, the Internet, alocal area network, wide area network and/or wireless network. Thenetwork may comprise copper transmission cables, optical transmissionfibers, wireless transmission, routers, firewalls, switches, gatewaycomputers and/or edge servers. A network adapter card or networkinterface card in each computing/processing device receives a programfrom the network and forwards the program for storage in acomputer-readable storage device within the respectivecomputing/processing device.

Computer program instructions for carrying out operations for aspects ofembodiments may be for example assembler code, machine code, microcodeor either source or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of embodiments are described below with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products according to embodiments of the invention. Itwill be understood that each block of the flowchart illustrations and/orblock diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions.

These computer program instructions may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer program instructions may also bestored in a computer readable storage medium that can direct a computer,other programmable data processing apparatus, or other devices tofunction in a particular.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

FIG. 9 shows a block diagram of an exemplary design flow 900 used forexample, in semiconductor IC logic design, simulation, test, layout, andmanufacture, such as incorporating the IC layout 124 of FIG. 1 into theDUT 112 of FIG. 1. Design flow 900 includes processes, machines and/ormechanisms for processing design structures or devices to generatelogically or otherwise functionally equivalent representations of thedesign structures and/or devices described above and shown in FIGS. 1-6.The design structures processed and/or generated by design flow 900 maybe encoded on machine-readable transmission or storage media to includedata and/or instructions that when executed or otherwise processed on adata processing system generate a logically, structurally, mechanically,or otherwise functionally equivalent representation of hardwarecomponents, circuits, devices, or systems. Machines include, but are notlimited to, any machine used in an IC design process, such as designing,manufacturing, or simulating a circuit, component, device, or system.For example, machines may include: lithography machines, machines and/orequipment for generating masks (e.g. e-beam writers), computers orequipment for simulating design structures, any apparatus used in themanufacturing or test process, or any machines for programmingfunctionally equivalent representations of the design structures intoany medium (e.g. a machine for programming a programmable gate array).

Design flow 900 may vary depending on the type of representation beingdesigned. For example, a design flow 900 for building an applicationspecific IC (ASIC) may differ from a design flow 900 for designing astandard component or from a design flow 900 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 9 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device, e.g., designstructures 200-600 of FIGS. 2-6 from IC layout 124 of FIG. 1 for DUT 112of FIG. 1. Design structure 920 may also or alternatively comprise dataand/or program instructions that when processed by design process 910,generate a functional representation of the physical structure of ahardware device. Whether representing functional and/or structuraldesign features, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer.

When encoded on a machine-readable data transmission, gate array, orstorage medium, design structure 920 may be accessed and processed byone or more hardware and/or software modules within design process 910to simulate or otherwise functionally represent an electronic component,circuit, electronic or logic module, apparatus, device, or system suchas those shown in FIGS. 1-6. As such, design structure 920 may comprisefiles or other data structures including human and/or machine-readablesource code, compiled structures, and computer-executable codestructures that when processed by a design or simulation data processingsystem, functionally simulate or otherwise represent circuits or otherlevels of hardware logic design. Such data structures may includehardware-description language (HDL) design entities or other datastructures conforming to and/or compatible with lower-level HDL designlanguages such as Verilog and VHDL, and/or higher level design languagessuch as C or C++. The design structure 920 may be stored in the memorysystem 106 of FIG. 1 and/or on the computer program product 800 of FIG.8.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 1-6 to generate a Netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including Netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information. Designprocess 910 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 1-6. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 1-6.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 1-6. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc. to finalize the DUT 112 of FIG. 1.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, or portion of code, whichcomprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

What is claimed is:
 1. A computer program product for implementingdesign-based weighting for logic built-in self-test (LBIST), thecomputer program product comprising: a non-transitory storage mediumreadable by a processing circuit and storing instructions for executionby the processing circuit for performing a method comprising: analyzing,by the processing circuit, a plurality of integrated circuit designorganizational units to determine preferred weightings of the integratedcircuit design organizational units that provide a highest level offailure coverage when applied to a random pattern generator; based ondetermining the preferred weightings, creating, by the processingcircuit, an integrated circuit layout comprising a plurality of weightedtest paths to respectively apply the preferred weightings to theintegrated circuit design organizational units, wherein the integratedcircuit design or organizational units are assignable to perform LBISTusing the preferred weightings as design-based weighting within a deviceunder test; and incorporating the integrated circuit layout in thedevice under test.
 2. The computer program product of claim 1, whereinthe instructions for execution by the processing circuit are furtherconfigured to assign the preferred weightings to multiplexer inputs forthe weighted test paths.
 3. The computer program product of claim 2,wherein the multiplexer inputs comprising the preferred weightings areassigned to a same multiplexer input position across a plurality ofmultiplexers such that selection of the same multiplexer input positionfor the multiplexers results in selecting the preferred weightingsacross the multiplexers.
 4. The computer program product of claim 3,wherein the instructions for execution by the processing circuit arefurther configured to connect a common weight selection register to atleast two of the multiplexers to enable selection of the samemultiplexer input position for the at least two of the multiplexers at asame time.
 5. The computer program product of claim 1, wherein each ofthe integrated circuit design organizational units is a Self-Test UsingMultiple Signal Registers and Pseudo-Random Pattern Generators (STUMPS)channel comprising a scan chain assigned to a macro, and the analyzingis performed on a STUMPS channel basis.
 6. The computer program productof claim 1, wherein the instructions for execution by the processingcircuit are further configured to modify at least one design file toannotate the preferred weightings of the integrated circuit designorganizational units in the at least one design file.
 7. The computerprogram product of claim 1, wherein the integrated circuit designorganizational units are macros, and the instructions for execution bythe processing circuit are further configured to assign an LBIST channelfor each unique instance of the preferred weightings and assign themacros to a corresponding LBIST channel based on the preferredweightings of the macros.
 8. A computer-implemented method forimplementing design-based weighting for logic built-in self-test(LBIST), the method comprising: analyzing, by a processing circuit, aplurality of integrated circuit design organizational units to determinepreferred weightings of the integrated circuit design organizationalunits that provide a highest level of failure coverage when applied to arandom pattern generator; based on determining the preferred weightings,creating, by the processing circuit, an integrated circuit layoutcomprising a plurality of weighted test paths to respectively apply thepreferred weightings to the integrated circuit design organizationalunits, wherein the integrated circuit design organizational units areassignable to perform LBIST using the preferred weightings asdesign-based weighting within a device under test; and incorporating theintegrated circuit layout in the device under test.
 9. Thecomputer-implemented method of claim 8, further comprising: assigningthe preferred weightings to multiplexer inputs for the weighted testpaths.
 10. The computer-implemented method of claim 9, wherein themultiplexer inputs comprising the preferred weightings are assigned to asame multiplexer input position across a plurality of multiplexers suchthat selection of the same multiplexer input position for themultiplexers results in selecting the preferred weightings across themultiplexers.
 11. The computer-implemented method of claim 10, furthercomprising: connecting a common weight selection register to at leasttwo of the multiplexers to enable selection of the same multiplexerinput position for the at least two of the multiplexers at a same time.12. The computer-implemented method of claim 8, wherein each of theintegrated circuit design organizational units is a Self-Test UsingMultiple Signal Registers and Pseudo-Random Pattern Generators (STUMPS)channel comprising a scan chain assigned to a macro, and the analyzingis performed on a STUMPS channel basis.
 13. The computer-implementedmethod of claim 8, further comprising: modifying at least one designfile to annotate the preferred weightings of the integrated circuitdesign organizational units in the at least one design file.
 14. Thecomputer-implemented method of claim 8, wherein the integrated circuitdesign organizational units are macros, and the method further comprisesassignin an LBIST channel for each unique instance of the preferredweightings and assign the macros to a corresponding LBIST channel basedon the preferred weightings of the macros.